Inflammation and cancer are linked by both oncogenic (intrinsic) and environmental (extrinsic) pathways (Yu et al., Nature Reviews Cancer 2009). The intrinsic pathway is activated by genetic or epigenetic alterations in transformed cells. Such alterations include those that cause the overexpression or the persistent activation of growth factor receptors with intrinsic tyrosine kinase activity and cytokine receptors with associated Janus kinase (JAK) family tyrosine kinases. Oncogenic mutations in receptor-associated JAK family members also underlie some types of cancer. These receptors, as well as non-receptor tyrosine kinases such as c-SRC, can be activated by extrinsic pathways—environmental factors that are associated with cancer inflammation—which include ultraviolet (UV) radiation, chemical carcinogens, infection, stress and cigarette smoke. Activated tyrosine kinases induced by both intrinsic and extrinsic pathways phosphorylate and activate the transcription factor signal transducer and activator of transcription 3 (STAT3), which in turn forms dimers that translocate to the nucleus, where they directly regulate the expression of a battery of target genes. In addition to upregulating numerous genes involved in proliferation, survival, invasion and metastasis, STAT3 induces the expression of many cytokines, chemokines and other mediators, such as interleukin-6 and cyclooxygenase 4 that are associated with cancer-promoting inflammation. Importantly, receptors for many of these cytokines, chemokines and mediators in turn further activate STAT3, thus forming autocrine and paracrine feedforward loops that result in a stable change to the genetic program and the promotion of cancer inflammation.
STAT3 is suggested to have a crucial role in selectively inducing and maintaining a procarcinogenic inflammatory microenvironment, both at the initiation of malignant transformation and during cancer progression. Persistent activation of STAT3 mediates the propagation of tumor-promoting inflammation and increases tumor cell proliferation, survival and invasion while suppressing anti-tumor immunity. Thus, STAT3 is an attractive molecular target for the development of novel cancer therapeutics or for modulating immune responses to improve cancer therapy.
Several small molecule inhibitors, that effectively block the STAT3 signaling pathway, are already known in the prior art (Deng et al., Current Cancer Drug Targets, 2007). These inhibitors, from a structural point of view, are divided into five classes of compounds. They include (1) natural products and derivatives, such as curcumin, resveratrol and others, (2) tyrphostins, (3) platinum-containing complexes, (4) peptidomimetics, and (5) azaspiranes.
It is also known from the prior art that instead of directly and specifically inhibiting STAT3, it is possible to effectively block the STAT3 signaling pathway by inhibiting the upstream targets. Indeed, as mentioned above, the STAT3 transcription factor is a downstream effector of both JAK and c-SRC kinases and is activated by tyrosine phosphorylation on tyrosine 705 (Y705) by these kinases, which is a prerequisite for STAT3 dimerization and activation of the transcription factor function of STAT3.
Thus c-SRC and JAK act upstream of the transcription factor STAT3, and their inhibition will lead to block STAT3 signaling pathway in a subset of STAT3 dependent tumors. It has been reported (Johnson et al., Clin. Cancer Res, 2007 and WO 2008/077062, Board of Regents, The University of Texas System) that c-SRC and JAK inhibitors have synergistic antitumor effects. Indeed, c-SRC can be rapidly and durably inhibited by, for example, Dasatinib, whereas STAT3 undergoes only transient inactivation. The addition of JAK inhibitors, such as pyridone 6 or AG490, during Dasatinib incubation resulted in sustained inhibition of STAT3, although JAK activation by Dasatinib was not shown. Combined c-SRC and JAK inhibition resulted in synergistic cytotoxicity due to increased apoptosis. Therefore with the combination treatment, the durable inhibition of several pathways, such as STAT3 signaling pathway, known to be important for cancer cell survival and proliferation can be obtained.
The SRC family of kinases (SFKs) is composed of nonreceptor tyrosine kinases with key roles in regulating signal transduction pathways that control cell proliferation, motility, adhesion and survival. SFKs and certain growth factor receptors are overexpressed in various cancers. Halpern M. S., England J. M., Kopen G. C, Christou A. A., Taylor R. L. Jr., Endogenous c-src as a Determinant of the Tumorigenicity of src Oncogenes, Proc Natl Acad Sd USA. 1996 93(2): 824-827. Haura, E. B., Zheng, Z., Song, L., Cantor, A., Bepler, G., Activated Epidermal Growth Factor Receptor-Stat-3 Signaling Promotes Tumor Survival In Vivo in Non-Small Cell Lung Cancer, Clin. Cancer Res. 2005, 11(23): 8288-8294. c-SRC plays a role in responses to regional hypoxia, limited nutrients, and internal cellular effects to self-destruct. Aberrant expression and/or activity of c-SRC are observed in numerous solid and liquid tumors, and play critical roles in affecting chemoresistance. Almost any growth factor leading to activation of receptor tyrosine kinases can be shown to activate c-SRC, making c-SRC a very attractive target for cancer therapy. Since the activation and perhaps over-expression of c-SRC has been implicated in cancer, osteoporosis, stroke, myocardial infarction, and vascular leak, among others, a small molecule inhibitor of c-SRC can be beneficial for the treatment of several disease states. However, inhibition of SFKs using a tyrosine kinase inhibitor has been shown to result in cytotoxicity, cell cycle arrest, and apoptosis in head and neck squamous carcinoma and non-small cell lung cancer cell lines. Johnson, F. M., Saigal, B., Talpaz, M., and Donate, N. J., Dasatinib (BMS-354825) Tyrosine Kinase Inhibitor Suppresses Invasion and Induces Cell Cycle Arrest and Apoptosis of Head and Neck Squamous Cell Carcinoma and Non-small Cell Lung Cancer Cells, Clin Cancer Res, 11: 6924-6932, 2005. In head and neck squamous carcinoma and non-small cell lung cancer cell lines, Dasatinib results in cytotoxicity, cell cycle arrest and apoptosis. However, despite the durable inhibition of SFKs and initial inhibition of STAT3, STAT3 is not durably inhibited.
The Janus kinases (JAKs) are cellular kinases and consist of four members—JAK1, JAK2, JAK3 and TYK2. The JAKs may play a crucial role in regulating cell behavior induced by a number of cytokines and are crucial components of diverse signal transduction pathways that govern cellular survival, proliferation, differentiation and apoptosis. The over-activation of JAK kinases has been implicated in tumorigenesis. In 2005, a recurrent mutation in JAK2 (JAK2V6I7F) leading to a constitutively active JAK2 was identified in a large number of patients with myeloproliferative disorders, including polycythaemia vera, essential thrombocythaemia and primary myelo fibrosis.
Several selective SRC family kinase inhibitors, such as SU6656, Dasatinib, WO 99/61444 (Warner-Lambert Company) or WO 2007/088014 (F. Hoffmann La Roche AG), and selective JAK inhibitors, such as pyridone 6, AG490 or those disclosed in WO 2009/054941 (Merck & Co., Inc), WO 2009/029998 (Cytopia Research PTY LTD) or WO/2008/157208 (Incyte Corporation), have been reported. SFKs also mediate STAT growth pathways in various cancers. Xi, S., Zhang, Q., Dyer, K. F., Lerner, E. C, Smithgall, T. E., Gooding, W. E., Kamens, J., and Grandis, J. R., Src kinases Mediate STAT Growth Pathways in Squamous Cell Carcinoma of the Head and Neck, J Biol Chem, 278: 31574-31583, 2003. An important need exists, therefore, for pharmaceutical composition and/or method of treatment for cancer that will inhibit both SFKs and STATs.
However there is a further need to develop a multi-targeted kinase inhibitor. A single compound which inhibits a combination of several targets, such as SFKs and JAKs, offers the advantage of inhibiting simultaneously several key signal transduction pathways, thereby interfering with several oncogenic processes, while making the treatment easier and improving the patients comfort. It would therefore be desirable to generate small molecule kinase inhibitor molecules able to simultaneously inhibit SFKs (in particular c-SRC) and JAKs.
By combining a dual inhibitory activity, such as SFKs (in particular c-SRC) and JAKs, in a single molecule, the advantage resides in (i) reducing the risks related to off-target toxicity encountered when two different kinase inhibitors targeting SFKs (in particular c-SRC) and JAKs are administered, (ii) reducing the costs of treatment, (iii) increasing the patients compliance, and (iv) blocking simultaneously parallel ways of activating the STAT3 pathway will lead to a better anti-tumoral response. Moreover, as the status of STAT3 activation can be monitored across tumor types, a multi SFKs (in particular c-SRC) and JAKs targeted kinase inhibitor could be used in various types of diseases based on the status of STAT3 in those tumors.
Accordingly, the present invention aims to provide compounds which simultaneously inhibit several key signal transduction pathways especially directed towards the status of STAT3 activation. Those compounds have the unexpected advantage to present either:                an inhibition for efficient STAT3 blockade following the inhibition of c-Src and JAK2;        an inhibition of STAT3 phosphorylation by in-cell Western preferably having an IC50≦500 nM;        in an established xenograft models using A431 and A549 (STAT3 positive cell lines) an inhibition of growth (>60%) of established tumors at a dose below MTD with a clear dose-response (highest dose close to MTD) and an inhibition of STAT3 phosphorylation in tumors.        
The compounds of the invention represent compounds showing a particular and unexpected good compromise between these 3 criteria.